Firing apparatus for explosives



Oct. 11, 1960 A. K. WOLFE FIRING APPARATUS FOR EXPLOSIVES Filed May 19, 1958 INVENTOR ANDREW K. WOLFE Patented Oct. 11,1960

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FIRING APPARATUS FOR EXPLOSIVES Andrew K. Wolfe, Philadelphia, Pa., assignor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed May 19, 1958, Ser. No. 736,123

Claims. ((11. 317-87 This invention relates to apparatus for causing flow of a predetermined quantity of electrical current for a predetermined period of time across a resistance element. The invention is especially adapted for use as a firing apparatus for laboratory bombs. The invention is, therefore, particularly concerned with firing apparatus for electrically fired bombs such as are used in the standard ASTM test for sulfur determination in petroleum products by the bomb method.

These bombs are fired by the passage of current A dilficult problem associated with the firing operation 35 is the avoidance of excessive firing current. This results from the fact that current of the same magnitude will not always be drawn by various bomb filaments with the application of a given voltage because of resistance differences in bomb ignition assemblies. Often the current is in excess of the tolerance limits of the filament, wherein the filament is destroyed. This has been a frequent experience in the past. a

It is not only desirable but essential that the ignition coil remain intact during the firing operation. important because the presence of disintegrated filament particles in the bomb following firing contaminates the test sample which can lead to erroneous test results. Furthermore, destruction of the ignition coil is costly and time-consuming since it must be replaced.

Despite the necessity for avoiding rupture of the filament by the firing current, it has been difficult to ac complish. This has been due largely to an unavailability of means for eifecting a precise control over the firing current in generally used ignition circuits.

I have now provided electrical apparatus that will deliver a predetermined quantity of electrical current for a predetermined period of time to a resistance element, such as the ignition filament of a laboratory bomb, to the exact degree desired without exceeding the current tolerance limits of the resistance element, and the present invention relates to such apparatus. Briefly, the apparatus of this invention comprises a normally open, resistance element-energizing circuit connected to a power source and containing the aforesaid resistance element, a first variable resistance to control the quantity of This is current passed through said resistance element-energizing circuit and switch means adapted to open and close said resistance element energizing circuit. The apparatus further comprises a current adjusting circuit, said current adjusting circuit being connected to said power source and being provided with a variable voltage-reducing bypass means, current indicating means, and a second'vari able resistance adapted to control the current passed through the current indicating means. The current adjusting circuit is provided with a shunt by-passing said current indicating means and also containing in series said first variable resistance which in this circuit is adapted'to control the quantity of current passed through the shunt. The variable resistance for controlling the quantity of current passed through the aforesaid shunt and said variable resistance adapted to control the quantity of current passed through said current indicating means are so connected that variation of the resistance in the shunt effects a direct variation in the quantity of current passed through the current indicating means. The device is further provided with switch means adapted to close the current adjusting circuit and the shunt circuit when the resistance element-energizing circuit is open and vice-versa.- The apparatus further comprises a normally open' timing circuit connected to said power source and containing switch actuating means associated with said switch means and adapted to open thecurrent adjusting circuit and to close the resistance elementenergizing circuit for a predetermined period oftime;

Referring now briefly to the drawing,- the single figure shows a schematic representation of the circuitry for a specific embodiment of the apparatus of this invention.

Referring nowto the drawing in greaterdetail, a

rectifier 12 is shown to be connected to A.C. power input terminals10 and 11. In series with rectifier 12 and forming a loop therewith are fixed resistor 13 and variable resistor 14. This arrangement provides a source of reduced voltage DC. power for the current adjusting circuit.

A first normally closed circuit is connected to the afore-mentioned loop through lead 16 which connects at the junction of resistances 13 and 14 and-through lead 15 which connects with the movable tap on resistance 14. This circuit, together with resistances 13 and 14, is re i'erred to hereinafter as the current adjustment circuit. In addition to resistances 13 and 14, the current adjustment circuit includes current indicating means, i.e. milliammeter 17, variable resistance 18, rheostat 19 and an ignition filament 39. Lead16 connects with one side of filament 39 through double-throw switch 20 when in normal position. The other side of filament 39 connects with the tap on variable resistor 18. Rheostat 19 is connected directly across filament 39 and the tap on variable resistor 18. The circuit bifurcates at the tap on variable resistor .18. One leg connects with milliammeter 17 through double-throw switch 21 when in normal position, while the other leg forms a current by-pass or shunt around milliammeter 17 through double-throw switch 22 in normal position. Both legs connect with the tap on resistor 14 at the junction of lead 15 and milliammeter 1 7. Switches 20, '21 and 22 constitute switch means for opening and closing the current adjusting circuit. Rheostat 19 and the left-hand portion in the drawing of vari able resistance 18 constitute a variable resistance adapted to control the current passed through the shunt and also through the resistance element-energizing or firing circuit, hereinafter described, when the resistances form a portion of the latter circuit. The right-hand portion in the drawing of variable resistance 18 constitutes a variable resistance to control the current passed through current indicating means 17. Rheostat 19 and the lefthand portion of resistance 18 are so connected with the right-hand portion of resistance 18 that a variation in the resistance in the shunt will effect a direct variation in the current passed through the current indicating means. While the current is shared between resistances 19 and 18, it is to be understood that resistance 19 will normally take by far the greater portion of such current, as will be clear from the specific embodiment described hereinafter.

Filament 39 does not draw sufiicient current with the current adjustment circuit closed to effect firing of the bomb. Since various bomb filaments and associated ignition elements will differ somewhat in electrical resistivity, this current will often vary from one bomb unit to another. However, the resistance in the circuit is calibrated through adjustments of rheostat 19 so that current of a predetermined magnitude will fiow through filament 39 as indicated by milliammeter 17.

Actuation of double-throw switches 20, 21, 22 and 23 opens the current adjacent circuit and closes a second or resistance element-energizing circuit, hereinafter referred to as the firing circuit. Switches 20, 22 and 23, therefore, constitute switch means for opening and closing the firing circuit. With the firing circuit closed, filament 39 receives A.C. power through the secondary of transformer 28 in sufficient magnitude to efiect firing of the bomb. Double-throw switch 23 when actuated connects the primary of transformer 28 with A.C. power input terminals and 11 through switch contact 27. Actuation of double-throw switches 20 and 22 places the secondary of transformer 28 in closed circuit relationship with the portion of variable resistor 18 that is to the left of the movable tap and with rheostat 19 and filament 39 through switch contacts 24 and 26. The portion of variable resistor 18 to the right of the movable tap, together with milliammeter 17, is eliminated from the circuit.

As noted, the resistance in the firing circuit is calibrated prior to use by means of the current adjustment circuit to permit a predetermined current flow through filament 39 when the firing circuit is closed. However, it is also necessary to fix in advance the time interval in which the firing circuit will be applied before firing in order to avoid destruction of the filament.

In order to actuate double-throw switches 20, 21, 22 and 23 so as to close the firing circuit for a predetermined time interval, a timing circuit containing switch actuating means is provided. This circuit includes capacitor 29 and coil 30. The coil 30 may be the actuating component of any suitable relay which has a switch actuating core member 31 adapted to actuate the movable contacts of double-throw switches 20, 21, 22 and 23. Coil 30 is in series with capacitor 29 and is energized by the discharge thereof. Connected across both the coil 30 and capacitor 29 in series arrangement are rheostat 32 and variable resistor 33. These components form a current by-pass around coil 30, thus shortening the time duration of coil operation by the extent of the resistance in or out of the circuit.

In order to charge the capacitor 29, a circuit is provided which when closed connects capacitor 29 with the DC. power of rectifier 12. Rectifier 12 connects with capacitor 29 through lead 34, contact 35 and switch 36. Switch 36 may be any suitable type with a movable contact such as a push-button switch as shown.

It will be seen that the capacitor charging circuit is closed by depressing push-button switch 36. The release of this switch opens the charging circuit, and the charge which has previously been built up across the plates of the capacitor immediately dissipates itself through the timing circuit as hereinabove described. The current which flows through relay coil 30' will cause the coil member 31 to move from a normally biased first position, which corresponds to the closed position for switches 20, 21 and 22 in the current adjusting position and the open position for these switches and for switch 23 in the firing circuit, to a second position, which corresponds to the open position for switches 20, 21 and 22 in the adjusting circuit and the closed position of these switches and switch 23 in the firing circuit. Thus, switches 20, 21, 22 and 23 become actuated and connect with contacts 24, 25', 26 and 27, whereupon the current adjustment circuit is opened and the firing circuit is closed.

In operation, the unit is made ready by connecting input terminals 10 and 11 to a suitable power source, generally with an availability of 110 volts of A.C. power. Pilot lamp 37 should light up indicating that the device is ready for use. A reading on milliammeter 17 is taken to determine the current flow through the bomb ignition system, While the current adjustment circuit is closed and the bomb cannot fire. If a predetermined value is not obtained, resistance changes are made by adjusting rheostat 19 until the desired value is obtained.

Before firing, adjustments are made in the timing circuit resistances 32 and 33. This will control the length of time in which the relay coil 30 will continue to operrate. With all the resistance in the circuit the time duration is greatest, and with all the resistance out of the circuit time duration is the shortest. Consequently, rheostat 32 is adjusted to the desired predetermined resistance value. The timing circuit is placed into operation by depressing push-button switch 36, whereupon capacitor 29 becomes charged. Upon release of pushbutton switch 36, capacitor 29 discharges and relay coil 30 becomes energized. The relay is thus caused to operate, whereupon the current adjustment circuit is opened and the firing circuit is closed. Current indicating lamp 38 should light up, indicating that the firing circuit is operating. The bomb has fired when indicated lamp 38 goes out.

In a specific embodiment of the invention, element 12 is a full wave selenium rectifier adapted to provide an output of 96 volts DC. to the timing circuit. Resistor 13 is of 10,000 ohm, 5 watt capacity, and variable resistor 14 is of 2,000 ohm, 25 watt capacity. Adjustment of the movable contact of resistor 14 provides the desired voltage drop across leads 15 and 16 of the current adjusting circuit. Transformer 28 is a 110 to 50 volt step-down transformer. Variable resistance 18 is of 20 ohm, 25 watt capacity, and rheostat 19 is of 4 ohm, 100 watt capacity. Milliammeter 17 is adapted to indicate fractions of a milli ampere. Coil 30 has a value of 10,000 ohms. Capacitor 29 has a 40 microfarad capacity. Variable resistor 33 is of 1,000 ohm, 25 watt capacity. Rheostat 32 is of 10,000 ohm, 50 watt capacity.

In a particular operation, terminals 10 and 11 are connected to a suitable volt A.C. power source, and the terminals of the current adjusting circuit are connected to the terminals of an ASTM sulfur bomb. At the outset, the movable tap on variable resistance 14 is adjusted so as to provide a 13.5 voltage drop between leads 15 and 16 of the current adjusting circuit. This voltage drop is sufiicient to calibrate the resistance of filament 39 on rheostat 19 without causing the bomb 40 to fire. Rheostat 19 is now adjusted until milliammeter 17 reads 0.2. milliampere. The timing circuit is now adjusted for the desired firing time, in this instance 0.5 second, by adjustment of rheostat 32. In the specific embodiment here described, the firing time duration is approximately 1.5 seconds when all the resistance is in the timing circuit, and only a few micro-seconds when all of the resistance is out of the timing circuit. .To

fire the apparatus, push-button switch depressed causing switches 20, 21, 22 and 23to open the current:

adjusting circuit and close the firing circuit for whatever period of time that has been determined by the setting of rheostat 32.

Although the herein described invention has been described particularly for use in connection with electrically fired laboratory bombs, it will be obvious that the apparatus can be equally useful in connection with any resistance element. For example, bomb 40 may be replaced by an infrared or an incandescent lamp, the illumination from which is to be controlled with great accuracy as in connection with photographic operations.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto, since many modifications may be made. I, therefore, contemplate by the appendant claims to cover any such modifications as fall within the true spirit and scope of my invention.

I claim:

1. Apparatus for causing flow of a predetermined quantity of electrical current for a predetermined period of time across a resistance element comprising: a normally open resistance element-energizing circuit connected to a power source and containing said resistance element, a first variable resistance to control the quantity of current passed through said resistance elementenergizing circuit and switch means adapted to open and close said resistance element-energizing circuit; a current adjusting circuit adapted quantitatively to vary the current passed through said resistance element-energizing circuit, said current adjusting circuit being connected to said power source and being provided with a variable voltage-reducing by-pass means, current indicating means and a second variable resistance adapted to control the current passed through the current indicating means, said current adjusting circuit also being provided with a shunt by-passing said current indicating means and containing in series said first variable resistance which in this circuit is adapted to control the quantity of current passed through said shunt, said first variable resistance for controlling the quantity of current passed through said shunt and said variable resistance adapted to control the quantity of current passed through said current indicating means being so connected that variation of the resistance adapted to control the quantity of current passed through said shunt effects a direct variation in the quantity of current passed through the current indicating means, and

switch means adapted to close the current adjusting circuit and the shunt when the resistance element-energizing circuit is open and vice-versa; a normally open timing circuit connected to said power source containing switch actuating means associated with said switch means and adapted to open the current adjusting circuit and to close the resistance element-energizing circuit for a predetermined period of time.

2. Apparatus for causing flow of a predetermined quantity of electrical current for a predetermined period of time across a resistance element comprising: a normally open resistance element-energizing circuit connected to a source of alternating current and contain-ing said resistance element, a first variable resistance to control the quantity of current passed through said resistance elemenu-energizing circuit, a transformer, switch means adapted to open and close said resistance element-energizing circuit and rectifying means connected to said source of alternating current; a current adjusting circuit, said current adjusting circuit being connected to said rectifying means and being provided with a variable voltage reducing by-pass means, current indicating means and a second variable resistance adapted to control the current passed through the current indicating means, said current indicating circuit also being provided with a shuntby-passingsaidcurrent indicating means. andcon-tg taining in, series said first variable resistance which inthis circuit is adapted to control the quantity of current; passed through said shunt, saidvariable resistance forcontrolling the quantity of current passed through said;

shunt and said variable resistance adapted to control the quantity of current passed through said current indicating means being so connected that variation of theresistance in the shunt effects a direct variation in the quantity, of current passed through the, current indicating means and switch means adapted to close the current adjusting circuit and the shunt circuit when the resistance elementenergizing circuit is open and vice-versa; a normally open timing circuit connected to said rectifying means and containing switch actuating means associated with said switch means and adapted to open the current adjusting circuit and to close the resistance element-energizing circuit for a predetermined period of time.

3. The apparatus of claim 2 where the resistance element-energizing circuit includes a variable resistance and said switch actuating means comprises a switch actuating member normally biased in one position that corresponds to the closed position for the switch means that arev adapted to open and close the current adjusting circuit and the shunt circuit and to the open position for the switch means adapted to open and close said resistance element-energizing circuit, said switch actuating means also comprising a coil for moving the switch actuating member to a second position corresponding to the open position for the switch means adapted to open and close the current adjusting circuit and to the closed position for the switch means adapted to open and close the resistance element-energizing circuit, a capacitor, means for connecting said capacitor to said rectifing means in order to charge said capacitor, means for disconnecting the capacitor from said rectifing means and for connecting said capacitor in series with said coil and with said variable resistance so that said capacitor will discharge through said coil and said variable resistance.

4. The combination of a laboratory bomb of the type which is fired by the passage of electric current through a filament contained therein with a firing apparatus comprising: adjustable resistance means connected to said filament, an alternating current power source, a current adjustment circuit including a rectifier, voltage dropping resistance and current indicating means, a plurality of double-throw switches which when in normal current adjusting position connect said adjustable resistance means and said filament to said power source through said current adjustment circuit wherein said filament draws insuificient current to cause firing of said bomb, a firing circuit including a transformer and switch contacts adapted for connection with said double-throw switches when actuated, means for actuating said doublethrow switches for a predetermined time interval wherein said current adjustment circuitis opened and said adjustable resistance means and said filament are connected to said power source through said firing circuit and wherein said filament draws a predetermined current of suflicient magnitude to fire said bomb.

5. A circuit for causing flow of electrical current of predetermined magnitude across a resistance element of unknovm impedance, comprising: a normally open, resistance element-energizing circuit connected to a power source and containing said resistance element, a first variable resistance to control the quantity of current passed through said resistance element-energizing circuit and switch means adapted to open and close said re-' sistance element-energizing circuit; a current adjusting circuit adapted quantitatively to vary the current passed through said resistance element-energizing circuit, said current adjusting circuit being connected to said power source and being provided with a variable voltage-re-- ducing by-pass means, current indicating means and a second variable resistance adapted to control the current passed through the current indicating means, said current adjusting circuit also being provided with a shunt by-passing said current indicating means and containing in series said first variable resistance which in this circuit is adapted to control the quantity of current passed through said shunt, said first variable resistance for controlling the quantity of current passed through said shunt and said variable resistance adapted to control the quantity of current passed through said current indicating means being so connected that variation of the resistance adapted to control the quantity of current passed through said shunt effects a direct variation in the quantity of current passed through the current indicating means, and switch means adapted to close the current adjusting circuit and the shunt when the resistance element-energizing circuit is open and vice-versa.

References Cited in the file of this patent UNITED STATES PATENTS Castel Mar. 1, 1955 

